Li Chang-Feng, Sureshkumar Radhakrishna, Khomami Bamin
School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, People's Republic of China.
Materials Research and Innovation Laboratory, Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Oct;92(4):043014. doi: 10.1103/PhysRevE.92.043014. Epub 2015 Oct 21.
Self-consistent direct numerical simulations of turbulent channel flows of dilute polymer solutions exhibiting friction drag reduction (DR) show that an effective Deborah number defined as the ratio of polymer relaxation time to the time scale of fluctuations in the vorticity in the mean flow direction remains O(1) from the onset of DR to the maximum drag reduction (MDR) asymptote. However, the ratio of the convective time scale associated with streamwise vorticity fluctuations to the vortex rotation time decreases with increasing DR, and the maximum drag reduction asymptote is achieved when these two time scales become nearly equal. Based on these observations, a simple framework is proposed that adequately describes the influence of polymer additives on the extent of DR from the onset of DR to MDR as well as the universality of the MDR in wall-bounded turbulent flows with polymer additives.
对呈现减阻（DR）的稀聚合物溶液湍流通道流进行自洽直接数值模拟表明，定义为聚合物松弛时间与平均流向涡度波动时间尺度之比的有效德博拉数从减阻开始到最大减阻（MDR）渐近线保持为O(1)。然而，与流向涡度波动相关的对流时间尺度与涡旋旋转时间之比随着减阻增加而减小，当这两个时间尺度变得几乎相等时达到最大减阻渐近线。基于这些观察结果，提出了一个简单的框架，该框架充分描述了聚合物添加剂对从减阻开始到最大减阻范围内减阻程度的影响，以及聚合物添加剂在壁面湍流中的最大减阻普遍性。
